Li Na

What we said: "A year ago she sounded weary of the expectations of being China's first great tennis player and her sardonic jokes about retiring cut a little too close to the bone. But after losing to Serena the three sets in the final of the WTA Championships, Li was practically upbeat and optimistic. I can't wait to see what she can do in 2014."

​What she's done: You can't say Li didn't deliver. Indeed, she built on that run to the final at the WTA Championships to go undefeated in January, winning the Shenzhen Open and then capturing the second Slam of her career at the Australian Open. As a result, she took over the No. 2 ranking ahead of Victoria Azarenka and looked poised for a run at No. 1 the rest of the year.

Her spring season was solid -- she had career-best results in both Indian Wells and Miami -- but everything fell apart at the French Open and Wimbledon, where she won just one match. Now, with news that Li and her coach Carlos Rodriguez have been forced to end their partnership due to his responsibilities at his Beijing tennis academy, it's hard to know how the rest of this year will pan out for her. At 32 years old, does she have the motivation to find a new coach and keep pushing herself? Is there even another coach on the planet who can connect with her the way Rodriguez did?

Agnieszka Radwanska

What we said: "She can come off as cold and emotionless on court, and I've heard fans complain about her lack of charisma and joy when she plays. But watching her slice, dice and out-think opponents is still one of my favorite things in tennis."

What she's done: Radwanska has been barely-there this season. Aside from her incredible performance in the Australian Open quarterfinals, where she beat Victoria Azarenka with a fun display of crafty shotmaking, the Pole hasn't made an impact.

The most disappointing aspect of Radwanska's season so far is that she's fallen short whenever a prime opportunity presented itself. After knocking out Azarenka in Australia to make her first Australian Open semifinal, she lost to Dominika Cibulkova 6-1, 6-2. Two months later she looked in position to win Indian Wells, and came up lame with injury in a 6-2, 6-1 loss to Flavia Pennetta. With her draw falling apart at Wimbledon, she lost 6-3, 6-0 to Ekaterina Makarova in the fourth round. Now she risks falling out of the top five for the first time since February 2012.

Petra Kvitova

​What we said: "She's a top three player if she can just get her game in order (her serve continues to be a mess) and play with a modicum of consistency (she has no idea where that forehand is going to go either), and she's the best bet when it comes to a player who can break up the stranglehold Serena and Victoria Azarenka have on the women's game."

What she's done: The same player who obliterated the draw at Wimbledon to capture her second Grand Slam with a memorable performance in a 6-3, 6-0 win in the final over Eugenie Bouchard also lost in the first round of the Australian Open to No. 88 LuksikaKumkhum. And that's everything you need to know about Kvitova. It's never been a question of whether she was good enough. Only whether she was consistent enough.

Simona Halep

What we said: "You always want to see if breakout players can follow it up."

What she's done: Halep did follow it up. Her 2013 success -- winning six titles -- meant she would be playing 2014 under pressure to match those results and defend her points. So far, so good. She's had career-best performances at all three majors -- Australian Open quarterfinals, French Open final and Wimbledon semifinals -- and won her biggest title at the Qatar Open in February. If not for Maria Sharapova, she probably would have won the French Open and Madrid, too. The Romanian is the real deal, and it's impressive how well she's handled the pressure.

Sloane Stephens

What we said: "A poor Grand Slam season and she could drop outside of the top 25. A good one, combined with improved play outside of the Slams and she's into the top 10 easily. But aside from wins, losses, and rankings, Stephens' public persona is still in flux after her controversial comments about Serena were published in the Spring. How her relationship with the fans and media evolves will be another element to watch."

What she's done: Stephens began the year ranked inside the top 15 -- she narrowly missed cracking the top 10 last year -- and now sits at No. 22. Her Grand Slam season wasn't a poor one, she made the fourth round at both the Australian Open and the French Open, but she still hasn't been able to crack the riddle that is her sub-par performance at the tour's regular tournaments. In the 14 tournaments she's played this year she's lost her opening match at six of them. Her partnership with Paul Annacone didn't yield results -- she is still the highest-ranked player without a title -- and she's now hired Thomas Hogstedt.

Sabine Lisicki

What we said: "But she has to figure out a way to bring her best tennis away from the All England Club. The first step is to stay healthy for a full season. The second step is entirely mental."

What she's done: It's been more of the same for Lisicki, who played her best tennis at Wimbledon to make her first and only quarterfinal of the season. That result kept her in the top 30. At the beginning of her career she showed she could be an all court player, having won tournaments on hard courts, grass, and clay. Now she's regressed into a one-tournament player. That's not sustainable.

Jamie Hampton

What we said: "Hampton finally came into her own in 2013, finishing as the No. 3 American and she'll be looking to prove that her season, in which she made her first WTA final at the AEGON International in Eastbourne, England, wasn't a fluke."

What she's done: Injuries have prevented Hampton from following up on her breakthrough season. She's played just one tournament, making the semifinals in Auckland before retiring and shutting down her season due to a hip injury.

Madison Keys

What we said: "While all of America is focused on Stephens as the American heir apparent, and Bouchard and Laura Robson as the teen queens, Keys can play without any external pressure or hype. 2013 was her first full-season on the WTA tour and she finished inside the top 40."

What she's done: It's been another year of slow and steady improvement for Keys. The 19-year-old cracked the top 30 last month after winning her first WTA tournament in Eastbourne and then making the third round of Wimbledon. Again, with the focus on Stephens and Bouchard, Keys has the luxury of working on her game in a relatively pressure-free environment. If she can build on her momentum from the grass season, a top-20 finish isn't out of the picture.

Venus Williams

What we said: "There is still some great tennis in her and while her physicality may be lacking, her competitive fire burns as bright as ever. She may lose, but she will battle."

​What she's done: She's still battling. It's been a very good season for Venus -- her best since being diagnosed with an auto-immune disease in 2011 -- and she's now up to No. 25 in the rankings. She won the Dubai Championships, made the final in Auckland, and was one-half of one of the best matches of the year, losing to Kvitova in the third round at Wimbledon. She still has to fight her body every day and can go through fits of poor play, but this has been an encouraging seven months for the seven-time Slam champion.

Monica Puig

What we said: "The 20-year old from Puerto Rico didn't finish the season strong, but for much of 2013 she was right in the conversation along with Bouchard, Robson, and Keys as part of the next generation of stars. She needs to get back into the mix."

What she's done: Injuries and coaching changes have taken the shine off Puig, who is down to No. 69 despite winning her first WTA title in Strasbourg in May. She split from Alain de Vos in the spring and teamed up with Antonio Van Grichen before Indian Wells, only to split with him and hire Ricardo Sanchez during the clay season. All the while the WTA's other young stars like Bouchard, Stephens, Keys and Muguruza have been grabbing headlines.